Base oils are used for the manufacture of lubricating oils for automobiles, such as engine oils and transmission oils, and for industrial uses, such as greases, process oils, white oils, and metal working oils. Lubricants are base oil formulations containing typically additives to enhance their properties for specific applications. Among the more commonly used additives in lubricant formulations are oxidation inhibitors, rust inhibitors, metal passivators, anti-wear agents, extreme pressure additives, pour point depressants, detergent-dispersants, viscosity index improvers, foam inhibitors and the like. Base oil is the major constituent in lubricant products and contributes significantly to the properties of the finished lubricant product.
Efforts to improve the performance of lubricants by providing hydrocarbon base oils with improved technical properties have been the subject of research and development work in the petroleum industry for several years. This is because new engine technologies require more robust lubricants than those based on conventional mineral oils. In terms of lubricant and thus base oil property improvement, industrial research has been toward fluids exhibiting useful viscosities over a wider range of temperature, i.e., improved viscosity index (VI), while also showing lubricity, thermal and oxidative stability and pour point equal to or better than mineral oil. These synthetic lubricants exhibit lower friction characteristics and they are therefore capable of increasing mechanical efficiency of various types of equipment including engines, transmissions, worm gears and traction drives, over a wider range of operating conditions than conventional mineral oil lubricants.
In addition to engine technology, also strict environmental requirements direct the industry to develop more sophisticated base oils. Sulphur free fuels and base oils are required in order to gain full effect of new and efficient anti-pollution technologies in modern vehicles and to cut emissions of nitrogen oxides, volatile hydrocarbons and particles, as well as to achieve direct reduction of sulphur dioxide in exhaust gases. The European Union has decreed that these fuels shall be available to the market from 2005 and they must be the only form on sale from 2009. Conventional mineral oil base oils contain sulphur, nitrogen, aromatic compounds, and typically also volatile compounds. They are less suitable for the new engines and thus also environmentally more detrimental than newer no-sulphur, no-aromatic base oils.
It can be assumed that the use of base oils, which are based on biological raw materials, will result in a significant reduction in carbon dioxide emissions. This is due to the closed carbon cycle of the renewable base oil. The CO2 released into the atmosphere when burning the base oil at the end of their lifecycle or due to oil loss by burning within the engine, is recycled by growing plants, which are later processed into base oil. As such, the increased use of base oils, which are based on biological material, represents an important step to meet the emission reduction target as agreed under the Kyoto agreement.
The increasing demand for high performance lubricants particularly requires high quality base oils. The American Petroleum Institute (API) classifies base oils according to the characteristics shown in Table 1. A similar classification is used also by the Association Technique de L'Industrie Européenne des Lubrifiants (or Technical Association of The European Lubricants Industry, ATIEL), containing also Group VI, polyinternalolefins (PIO). In the classification, the term “saturates” includes both paraffinic and naphthenic compounds but not aromatic compounds.
API 1509 defines a base stock as: “A base stock is a lubricant component that is produced by a single manufacturer to the same specifications (independent of feed source or manufacturer's location); that meets the same manufacturer's specification; and that is identified by a unique formula, product identification number, or both. Base stocks may be manufactured using a variety of different processes including but not limited to distillation, solvent refining, hydrogen processing, oligomerization, esterification, and rerefining. Rerefined stock shall be substantially free from materials introduced through manufacturing, contamination, or previous use.” Base oil is the base stock or blend of base stocks used in API-licensed oil.
Generally lubricating base oils are base oils having kinematic viscosity of about 3 mm2/s or greater at 100° C. (KV100, kinematic viscosity measured at 100° C.); a pour point (PP) of about −12° C. or less; and a viscosity index (VI) about 120 or greater. The oils in Group III are very high viscosity index (VHVI) base oils, which are manufactured from crude oil by hydrocracking and catalytic dewaxing or solvent dewaxing. Group III base oils can also be manufactured by catalytic dewaxing of slack waxes originating from crude oil refining, or by catalytic dewaxing of waxes originating from Fischer-Tropsch synthesis from natural gas or coal based raw materials. Group IV base oils are polyalpha-olefin (PAO) base oils.
TABLE 1API-classification of base oilsSulphur/wt-%ViscositySaturates/wt-%(ASTM D 1552/D 2622/Dindex (VI)Group(ASTM D 007)3120/D 4294/D 4927)(ASTM D 2270)I<90 and/or>0.03 80 ≦ VI < 120II≧90≦0.03 80 ≦ VI < 120III≧90≦0.03120 ≦ VIIVAll polyalpha-olefins (PAO)VAll other base oils not included in Groups I-IV
Fatty acids have been used as raw materials in various applications in chemical industry, typically in the manufacture of products ranging from lubricants, polymers, fuels and solvents to cosmetics. Fatty acids are generally obtained from wood pulping processes or by hydrolysis of triglycerides of vegetable or animal origin. Naturally occurring triglycerides are usually esters of glycerol and straight chain even numbered carboxylic acids having 10-26 carbon atoms. Most common fatty acids contain 16, 18, 20 or 22 carbon atoms. Fatty acids may either be saturated or they may contain one or more unsaturated bonds. Unsaturated fatty acids are often olefinic having carbon-carbon double bonds with cis configuration. The unsaturated centers appear in preferred positions in the carbon chain. The most common position is ω9, like in oleic acid (C18:1) and erucic acid (C22:1). Polyunsaturated acids generally have a methylene-interrupted arrangement of cis-olefinic double bonds.
Conventional base oils of biological origin comprise esters and their use is limited to specific applications, such as refrigeration compressor lubricants, bio-hydraulic oils and metal working oils. As polar compounds, esters suffer greater seal-swelling tendency than hydrocarbons when used as engine oils. In hydraulic applications, esters are not suitable for use together with hose elastomers. In addition, the esters used in engine oil formulations are not interchangeable with other esters without performing new engine tests. Instead, base oils consisting of pure hydrocarbon structure are partly interchangeable with each other. Ester base oils are hydrolyzed easily producing acids, corroding lubricating systems when used as engine oils. Further, even greater disadvantage of esters is that additives developed for non-polar hydrocarbon base oils are not effective for ester base oils. A further major disadvantage of synthetic esters is that they are inherently more expensive than high quality mineral base oils.
The need of high quality base oils has led to the introduction of a number of polyalpha-olefin based synthetic lubricants produced by oligomerization of alpha-olefins (1-alkenes). Polyalpha-olefins, useful as synthetic base oils may be synthesized by homogeneous Friedel-Crafts catalyst such as BF3 or AlCl3, typically followed by hydrogenation to stabilize the oligomer against oxidation and degradation. In a typical polyalpha-olefin production process, 1-decene is used as the starting material. Polymers of 1-decene and mixtures of 1-decene with 1-octene and/or 1-dodecene generally result in base oils having a high viscosity index (VI) and low pour point. Polyalpha-olefins are useful as base oils for lubricants, transmission fluids, and transformer fluids.
Typically highly saturated polyalpha-olefin base oils contain very low levels of cycloparaffins and highly saturated VHVI base oils contain high levels of multicycloparaffins. A certain amount of monocycloparaffins is desired in base oils to provide adequate additive solubility and elastomer compability. Multicycloparaffins are less desirable than monocycloparaffins due to their poorer viscosity index, lower oxidation stability, and increased Noack volatility.
Olefins having from about 5 to about 20 carbon atoms are prepared by a number of methods including thermal and catalytic cracking of petroleum fractions, thermal cracking of paraffin wax, dehydrochlorination of monochlorinated paraffinic hydrocarbons, polymerization of low molecular weight olefins by the Ziegler process, hydrogenation of fatty acids to alcohols with subsequent dehydration of alcohols to olefins, and hydrogenation of fatty acid esters or triglycerides to paraffins with subsequent dehydrogenation of paraffins to olefins.
Fatty alcohols can be produced on commercial scale by hydrogenolysis, or in other words by hydrogenation of fatty esters, fatty acids or triglycerides. In the fatty ester route, the preparation of an intermediate methyl ester or wax ester product is used. U.S. Pat. No. 5,608,122 discloses a process for preparing wax esters (or fatty esters) and subsequent hydrogenation of wax esters to fatty alcohols. In the esterification step, fatty acids and fatty alcohols are esterified at a temperature of 120-320° C. in the excess of circulating fatty alcohol without catalyst. The intermediate wax ester product is hydrogenated at 100-300° C. under a pressure of 20-40 MPa using conventional copper-chromite or copper catalysts to produce fatty alcohol.
Direct hydrogenation of fatty acids to produce fatty alcohols is not that widely used due to need of higher reaction temperatures resulting in lower yields, and due to damaging effects of fatty acids on the catalyst. In direct hydrogenation process of triglycerides to fatty alcohols, in addition to fatty alcohols and glycerol also propane diol and propanol are obtained as the over-reduction products of glycerol. U.S. Pat. No. 6,683,224 teaches a process for the continuous production of fatty alcohols by the hydrogenation of naturally occurring fats, oils and fatty derivatives in a fixed-bed reactor at a temperature 160-320° C. under a pressure of 5-30 MPa in the presence of at least stoichiometric amount of hydrogen. In the process both the ester groups and also carbon double bonds are hydrogenated on the copper-containing catalyst to form saturated fatty alcohols, even in cases where unsaturated esters are used as feedstock.
Dehydration of alcohols to form olefins is one of the oldest catalytic reactions, and numerous oxides are suitable catalysts for this reaction. Activated alumina is the primary industrial catalyst, typical conditions being atmospheric pressure, temperature of 250-400° C. and 1-5 m3 of liquid per h/m3 of catalyst. DE 3,915,493 discloses a process for dehydration of fatty alcohols under normal pressure and at a temperature of 280-300° C. in vapor phase. WO 01/44145 describes a dehydration process to convert C4-C40 alcohols to olefins by a zirconium oxide on aluminium oxide catalyst.
U.S. Pat. No. 4,554,397 discloses a process for the manufacture of linear olefins from saturated fatty acids or esters by decarboxylation, using a catalytic system consisting of nickel and at least one metal selected from the group consisting of lead, tin and germanium. Additives may be included in the above-mentioned catalysts and for example sulphur derivatives may be added to decrease the hydrogenating power of nickel and to improve the selectivity for olefin formation reaction. The presence of hydrogen is necessary to maintain the activity of the catalyst. The reaction is carried out at a temperature of 300-380° C. and the pressure is atmospheric pressure or higher. This reaction is applicable particularly to saturated linear carboxylic acids having from 6 to 30 carbon atoms, as well as to esters formed form said acids and mono- or polyhydric alcohol.
U.S. Pat. No. 5,597,944 discloses a process for producing n-olefins via dehydrogenation of C5 to about C20 n-paraffins by dehydrogenating in the presence of manganese oxide octahedral molecular sieve as catalyst. The presence of hydrogen is necessary to prevent coking of the catalyst. Reaction temperatures for the catalytic dehydrogenation of n-paraffin hydrocarbons range from about 100° C. to about 750° C. Since the dehydrogenation reaction is endothermic, heat must be continually added to the reaction in order to maintain the reaction.
A conventional route to prepare 1-decene and other linear alpha-olefins is via oligomerisation of ethylene using an alkylated metal catalyst, also resulting in a wide spectrum of products having even-numbered carbon chain lengths. Polymerization of ethylene usually produces a wide range of alpha-olefins, from 1-butene to 1-C20 and higher alpha-olefins, with the product distribution governed by the degree of polymerization. The higher alpha-olefins, such as C14 or higher, generally are not used as starting materials for polyalpha-olefin production because the resulting polymers typically have undesirable properties such as high pour point and high volatility that render them unsuitable for use as high performance base oils.
U.S. Pat. No. 4,218,330 presents a process for oligomerising higher olefins such as C12-C18 with homogeneous cationic catalysts, such as boron trifluoride, to form lubricant products. Polyalpha-olefin processes using homogeneous catalysts always include a complicated and tedious catalyst separation step.
U.S. Pat. No. 3,322,848 discloses a method of manufacturing lubricating oils from C10-C18 alpha-olefins using a microporous catalytic agent prepared by base exchanging a crystalline alkali metal aluminosilicate having uniform pore openings of 6 to 15 Ångström units with an ionisable metal compound, such as rare earth metals. This process generally resulted in low lube yields and significant amounts of coke formation. Furthermore, the products made from 1-dodecene or 1-tetradecene had relatively high pour points.
U.S. Pat. No. 5,453,556 provides an oligomerisation process where a catalyst comprising an acidic solid comprising a Group IVB metal oxide, such as zirconia, modified with an oxyanion of a Group VIB metal, such as tungsten, is used. A C6-20 alpha-olefin feedstock is contacted with the oligomerisation catalyst under a reaction temperature between 20° C. to 250° C.
U.S. Pat. No. 6,703,356 discloses conversion of higher olefins using high activity crystalline zeolite catalysts with widely open structures and having high activity for polymerization. In addition, mixed oxide catalysts, such as WOx/ZrO2, and acid clay catalysts may also be used. The polyolefins produced in accordance with the processes have low viscosity, volatility, and pour point characteristics when compared to conventional polyalpha-olefins formed from C8-C12 olefins.
Based on the above, it can be seen that here is a need for a new alternative process for the preparation of saturated and branched hydrocarbons from renewable sources suitable as high quality base oil.